Method of and device for cooling brake fluid

ABSTRACT

A method of cooling a brake fluid using a brake operating unit which comprises a first and a second flow channels connected to a cylinder of a brake element at one ends thereof comprises a step of setting the absolute value of a difference between the amount of brake fluid supplied to and that discharged from the cylinders in the first flow channel to apply and release brakes respectively equal to the absolute value of a difference between the amount of the brake fluid supplied to and that discharged from the cylinder in the second flow channel to apply and release the brakes respectively, so as to circulate the brake fluid in the cylinder using both of the first and second flow channels by repetition of applying and releasing the brakes. As a result, it is possible to provide a method of and a device for cooling a brake fluid, wherein vapor-lock can be prevented with certainty, the brake element that is a drum brake or a disc brake is improved in safety and reliability, friction materials such as brake shoes or pads are restrained from rising in temperature and a fade phenomenon is also reduced so that a stable braking operation can be obtained.

This is a division of Ser. No. 08/521,057, filed Aug. 29, 1995, now U.S.Pat. No. 5,954,166.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and a device for cooling abrake fluid.

2. Prior Art

There is known a conventional brake operating unit comprising a brakeelement that is a drum brake or a disc brake. That is, a fluid (liquid)pressure generating unit composed of, e.g., a master cylinder isactuated by depressing a brake pedal to supply a brake fluid to acylinder of the brake element, the amount of the brake fluidcorresponding to the depressed amount of the brake pedal, so as togenerate a braking force, or the fluid pressure generating unit isreleased by releasing the brake pedal from being depressed to dischargethe brake fluid in the cylinder of the brake element so as to releasethe braking force. At the time of releasing the brakes, the brake fluidin the cylinder of the brake element is discharged therefrom by theelastic restoring force of a shoe return spring in case of a drum brake,and by that of a seal ring in case of a disc brake. The brake elementgenerates a braking force when friction materials of brake shoes or padsslidably contacts a brake drum or disc while generating a frictionalheat.

In such a conventional brake operating unit, however, only a singlebrake line (fluid channel) is connected to the cylinder of brake elementfor both supply and discharge of the brake fluid, so that the brakefluid only moves into or out of the cylinder therethrough but it is notsubstantially exchanged with a brake fluid of low temperature. As aresult, frequent repetition of applying the brakes generates avapor-lock to cause a dangerous state of brake failure. The vapor-lockis a phenomenon caused by the failure of normal transmission of pressurewhen the brake fluid in the cylinder of a brake element is overheated sothat a part of it is vaporized and gasified. Although it is proposed tocool the brake element by sending air thereto for preventing thevapor-lock, a brake element which can prevent the vapor-lock withcertainty has not appeared yet.

SUMMARY OF THE INVENTION

The present invention has been made in view of such a problem of theconventional technology to provide a method of cooling a brake fluid anda device used therein as follows.

A method of cooling a brake fluid using a brake operating unit whichcomprises a first and a second flow channels 2 and 3 connected to acylinder 1 or 20 of a brake element at one ends thereof according to afirst aspect of the invention is characterized in comprising a step ofsetting the absolute value of a difference between the amount of brakefluid supplied to and that discharged from the cylinder 1 or 20 in thefirst flow channel 2 to apply and release the brakes respectively equalto the absolute value of a difference between the amount of brake fluidsupplied to and that discharged from the cylinder 1 or 20 in the secondflow channel 3 to apply and release the brakes respectively so as tocirculate the brake fluid in the cylinder 1 or 20 using both of thefirst and second flow channels 2 and 3 by repetition of applying andreleasing the brakes.

A device for cooling a brake fluid according to a second aspect of theinvention is that of the first aspect of the invention characterized inthat the cylinder 20 is of plural-pot type for a disc brake that is abrake element.

A device for cooling a brake fluid according to a third aspect of theinvention is that of the first aspect of the invention characterized inthat at least one of the first and second flow channels 2 and 3 iscomposed of a plurality of lines.

A device for cooling a brake fluid according to a fourth aspect of theinvention is characterized in that one ends of a first flow channel 2and a second flow channel 3 are connected to a cylinder 1 or 20 of abrake element while the other ends thereof are connected to a fluidpressure generating unit 5 which generates fluid pressure in accordancewith a depressed amount of a brake pedal 15 and at least one of thefirst and second flow channels 2 and 3 is provided with at least a means7, 10, 11, or 12 and 13 for generating a difference between the amountof brake fluid supplied to and that discharged from the cylinders 1 or20 to apply and release the brakes respectively, wherein the absolutevalue of a difference between the amount of the brake fluid supplied toand that discharged from the cylinder 1 or 20 in the first flow channel2 to apply and release the brakes respectively is made equal to theabsolute value of a difference between the amount of the brake fluidsupplied to and that discharged from the cylinder 1 or 20 in the secondflow channel 3 to apply and release the brakes respectively so as tocirculate the brake fluid in the cylinder 1 or 20 using both of thefirst and second flow channels 2 and 3.

A device for cooling a brake fluid according to a fifth aspect of theinvention is that of the fourth aspect of the invention characterized inthat the other ends of both of the first and second flow channels 2 and3 are connected to the fluid pressure generating unit 5 by way of a mainfluid channel 6.

A device for cooling a brake fluid according to a sixth aspect of theinvention is that of the fourth aspect of the invention characterized inthat at least a tank 8 is interposed in a channel composed of the firstand second flow channels 2 and 3 for storing the brake fluid whichcirculates in the first and second flow channels 2 and 3, the tank 8forming a part of the channel.

A device for cooling a brake fluid according to a seventh aspect of theinvention is that of the fourth aspect of the invention characterized inthat the first and second flow channels 2 and 3 are connected to eachother at least at one end portions thereof by way of at least aconnecting member 84 or 84₁ to 84₆ or 84a and 84b.

A device for cooling a brake fluid according to an eighth aspect of theinvention is that of the fourth aspect of the invention characterized inthat the cylinder 20 is of plural-pot type for a disc brake that is abrake element.

A device for cooling a brake fluid according to a ninth aspect of theinvention is that of the sixth aspect of the invention characterized inthat at least one of tanks 8 comprises a tank body 80 which is dividedinside into a plurality of liquid chambers 80a(, 80b) and 80c by atleast a partition 81 (and 82) having at least an opening portion 81a(and82a respectively), wherein neighboring liquid chambers 80a and (80b or80b and) 80c are communicated with one another by way of the openingportion 81a (and 82a), the liquid chamber 80a located at one end of thetank body 80 is connected to a hot side of one of the first and secondflow channels 2 and 3 while the liquid chamber 80c located at the otherend of the tank body 80 is connected to a cool side of one of the firstand second flow channels 2 and 3.

A device for cooling a brake fluid according to a tenth aspect of theinvention is that of the sixth aspect of the invention characterized inthat the means 7, 10, 11, or 12 and 13 is attached to the tank 8.

A device for cooling a brake fluid according to an eleventh aspect ofthe invention is characterized in that one ends of a first flow channel2 and a second flow channel 3 are connected to a cylinder 1 or 20 of abrake element, the other end of the first flow channel 2 is connected toa fluid pressure generating unit 5 which generates fluid pressure inaccordance with the depressed amount of a brake pedal 15 and the otherend of the second flow channel 3 is connected to the first flow channel2 and a pump 33 is interposed in the second flow channel 3 thereby tocirculate brake fluid in the cylinders 1 or 20 using both of the firstflow channel 2 and the second flow channel 3 by actuating the pump.

A device for cooling a brake fluid according to a twelfth aspect of theinvention is that of the eleventh aspect of the invention characterizedin that a closing valve unit 34 is provided for both of an inlet 33aside of the pump 33 and an outlet 33b side of the pump 33, the closingvalve unit 34 being open at a time of actuating the pump 33 concurrentlyat both sides thereof.

A device for cooling a brake fluid according to a thirteenth aspect ofthe invention is that of the eleventh aspect of the inventioncharacterized in that the other ends of both of the first and secondflow channels 2 and 3 are connected to the fluid pressure generatingunit 5 by way of a main fluid channel 6.

A device for cooling a brake fluid according to a fourteenth aspect ofthe invention is that of the eleventh aspect of the inventioncharacterized in that at least a tank 8 is interposed in a channelcomposed of the first and second flow channels 2 and 3 for storing thebrake fluid which circulates in the first and second flow channels 2 and3, the tank 8 forming a part of the channel.

A device for cooling a brake fluid according a fifteenth aspect of theinvention is that of the eleventh aspect of the invention characterizedin that the first and second flow channels 2 and 3 are connected to eachother at least at one end portions thereof by way of at least aconnecting member 84 or 84₁ to 84₆ or 84a and 84b.

A device for cooling a brake fluid according to a sixteenth aspect ofthe invention is that of the eleventh aspect of the inventioncharacterized in that the cylinder 20 is of plural-pot type for a discbrake that is a brake element.

A device for cooling a brake fluid according to a seventeenth aspect ofthe invention is that of the twelfth aspect of the inventioncharacterized in that the closing valve unit 34 is divided into aclosing valve for closing an inlet 33a side of the pump 33 and a closingvalve for closing an outlet 33b side of the pump 33.

A device for cooling a brake fluid according to an eighteenth aspect ofthe invention is that of the fourteenth aspect of the inventioncharacterized in that at least one of tanks 8 comprises a tank body 80which is divided inside into a plurality of liquid chambers 80a(, 80b)and 80c by at least a partition 81 (and 82) having at least an openingportion 81a (and 82a respectively), wherein neighboring liquid chambers80a and (80b or 80b and )80c are communicated with one another by way ofthe opening portion 81a (and 82a), the liquid chamber 80a located at oneend of the tank body 80 is connected to a hot side of one of the firstand second flow channels 2 and 3 while the liquid chamber 80c located atthe other end of the tank body 80 is connected to a cool side of one ofthe first and second flow channels 2 and 3.

A device for cooling a brake fluid according to a nineteenth aspect ofthe invention is characterized in that one end of a main fluid channel 6is connected to a cylinder 1 or 20 of a brake element and the other endof the main fluid channel 6 is connected to a fluid pressure generatingunit 5 which generates liquid pressure in accordance with the depressedamount of a brake pedal 15, while a fluid supply and discharge tank 18is provided at a middle portion of the main fluid channel 6 to form apart of the main fluid channel 6 so as to divide the main fluid channel6 into a first main fluid channel 6a and a second fluid channel 6b,which are disposed between the cylinder 1 or 20 and the fluid supply anddischarge tank 18 and between the fluid supply and discharge tank 18 andthe fluid pressure generating unit 5 respectively, wherein a capacity Dof the first main fluid channel 6a is set to a size which allows a partof brake fluid which is actually discharged from the cylinder 1 or 20 ata time of releasing brakes to flow into the fluid supply and dischargetank 18 and a capacity C of the fluid supply and discharge tank 18 isset to a size which is not filled with a brake fluid which is actuallydischarged from the cylinder 1 or 20 at a time of releasing the brakes.

According to the invention described in the first and fourth aspects ofthe invention, since the amount of brake fluid supplied to the cylinder1 or 20 is equal to that discharged therefrom at the time of operatingthe brake, the following functions can be obtained. Applying andreleasing (taking off) the brakes generate a difference between theamount of the brake fluid supplied to and that discharged from thecylinder 1 or 20 accompanying the application and release of the brakesrespectively through the first flow channel 2 and a difference betweenthe amount of the brake fluid supplied to and that discharged from thecylinder 1 or 20 accompanying the application and release of the brakesrespectively through the second flow channel 3. Since both of thedifferences are equal to each other in absolute value, if they are notzero, the repetition of operating the brake circulates the brake fluidin the cylinder 1 or 20 of a brake element through both of the first andsecond flow channels 2 and 3 for operating the brake. When the brakefluid circulates in the first and second flow channels 2 and 3, it iscooled by air. As a result, it is almost certain that the brake fluid inthe cylinder 1 or 20 of the brake element is prevented from beingoverheated by heat generated accompanying the operation of the brakes.

According to the second aspect of the invention, in a disc brake that isa brake element, the plural-pot type cylinder 20 can obtain a functionsimilar to the first aspect of the invention with regard to circulatingand cooling the brake fluid.

According to the third aspect of the invention, the brake fluid flows inthe first and/or second flow channel 2 and/or 3, one being composed of aplurality of lines. As a result, they function similar to the firstaspect of the invention with regard to circulating and cooling the brakefluid.

According to the fifth aspect of the invention, the brake fluid from thefluid pressure generating unit 5 is pushed out into the main fluidchannel 6 and the first flow channel 2 or the second flow channel 3 andcirculates therethrough. As a result, a function similar to the fourthaspect of the invention can be obtained with respect of circulating andcooling the brake fluid.

According to the sixth aspect of the invention, when the brake fluidcirculates in the first flow channel 2 and the second flow channel 3, itis temporarily stored in the tank 8 which forms a part of the channel.The presence of the tank 8 increases the amount of the brake fluid toalmost certainly prevent the brake fluid in the cylinder 1 or 20 frombeing overheated by heat generated accompanying the operation of thebrakes even if the first and second flow channels 2 and 3 are madeshort.

According to the seventh aspect of the invention, the connecting member84, or 84₁, 84₂, 84₃, 84₄, 84₅, 84₆, or 84a and 84b which keeps thefirst and second flow channels 2 and 3 apart from each other leaving agiven space at least at one end portions thereof to prevent friction andabrasion therebetween.

According to the eighth aspect of the invention, in the disc brake thatis a brake element, the plural-pot type cylinder 20 can obtain afunction similar to that of the fourth aspect of the invention withrespect to circulating and cooling the brake fluid.

According to the ninth aspect of the invention, the circulating brakefluid flows into the liquid chamber 80a located at one end of the tankbody 80 of the tank 8 from the first flow channel 2 or the second flowchannel 3 at the hot side, reaches the liquid chamber 80c located at theother end of the tank body 80 through the opening portion 81a (and 82a)of the partition 81 (and 82) and flows from the liquid chamber 80c intothe first flow channel 2 or the second flow channel 3 at the cool sidetoward the cylinder 1 or 20. Accordingly, the brake fluid which has beencooled by air in the tank body 80 of the tank 8 is gradually reduced intemperature as it flows in the liquid chambers 80a(, 80b) and 80c andthe eventually cooled brake fluid flows into the first flow channel 2 orthe second flow channel 3 at the cool side. As a result, the cool brakefluid flows into the cylinder 1 or 20 so that the brake fluid in thecylinder 1 or 20 is effectively prevented from being overheated by heatgenerated accompanying the operation of the brakes.

According to the tenth aspect of the invention, the means 7, 10, 11, or12 and 13 provided at least in one of the first and second flow channels2 and 3 of the above fourth aspect of the invention is attached to thetank 8 of the sixth aspect of the invention. As a result, it is possibleto make the brake operating unit compact in size.

According to the eleventh aspect of the invention, the followingfunction can be obtained. When the pump 33 is actuated, the brake fluidin the cylinder 1 or 20 flows through the first flow channel 2 and thesecond flow channel 3 and gradually flows back to the cylinder 1 or 20.Accordingly, it is possible to circulate the brake fluid in the cylinder1 or 20 through both of the first flow channel 2 and the second flowchannel 3.

As described above, the brake fluid which serves in the cylinder 1 or 20for operating the brake is cooled by air as it passes through the firstflow channel 2 and the second flow channel 3, so that it is preventedfrom being overheated by heat accompanying the application of thebrakes. Since the replaced amount of the brake fluid in the cylinder 1or 20 depends on time during which the pump 33 is operated, it is almostcertain to prevent the brake fluid in the cylinder 1 or 20 from beingoverheated by adjusting the operating time of the pump 33.

According to the twelfth aspect of the invention, since the closingvalve unit 34 is open when the pump 33 is operated, the brake fluidwhich has entered the pump 33 through the inlet 33a thereof isdischarged from the outlet 33b for circulation. The circulation of thebrake fluid is stopped with certainty by closing the closing valve unit34 when the operation of the pump 33 is stopped.

According to the thirteenth aspect of the invention, the brake fluidfrom the fluid pressure generating unit 5 is pushed out into the mainfluid channel 6 and the brake fluid in the main fluid channel 6 issupplied to the cylinder 1 or 20 through the first flow channel 2 toobtain a braking force.

According to the fourteenth aspect of the invention, when the brakefluid circulates in the first flow channel 2 and the second flow channel3, it is temporarily stored in the tank 8 which forms a part of thechannel. The presence of the tank 8 increases the amount of the brakefluid to almost certainly prevent the brake fluid in the cylinder 1 or20 from being overheated by heat generated accompanying the operation ofthe brakes even if the first and second flow channels 2 and 3 are madeshort.

According to the fifteenth aspect of the invention, the connectingmember 84 or 84₁, 84₂, 84₃, 84₄, 84₅, 84₆, or 84a and 84b which keepsthe first and second fluid channels 2 and 3 apart from each otherleaving a given space at least one end portions thereof to preventfriction and abrasion therebetween.

According to the sixteenth aspect of the invention, in the disc brakethat is a brake element, the plural-pot type cylinder 20 can obtain afunction similar to that of the eleventh aspect of the invention withrespect to circulating and cooling the brake fluid.

According to the seventeenth aspect of the invention, a pair of closingvalves function similarly to the closing valve unit 34 of the twelfthaspect of the invention. As a result, a function similar to that of thetwelfth aspect of the invention can be obtained.

According to the eighteenth aspect of the invention, a function similarto that of the ninth aspect of the invention can be obtained with regardto the tank 8. As a result, the cool brake fluid flows into the cylinder1 or 20 so that the brake fluid in the cylinder 1 or 20 is effectivelyprevented from being overheated by heat generated accompanying theoperation of the brakes.

According to the nineteenth aspect of the invention, when the brakepedal 15 is depressed, the brake fluid pushed out into the main fluidchannel 6 from the fluid pressure generating unit 5 flows into thecylinder 1 or 20 by way of a second main fluid channel 6b, the fluidsupply and discharge tank 18 and a first main fluid channel 6a. At thattime, a part of the brake fluid in the fluid supply and discharge tank18 actually flows into the cylinder 1 or 20.

Thereafter, when the brake is released, the brake fluid flows back fromthe cylinder 1 or 20 toward the fluid pressure generating unit 5. Atthat time, a part of the brake fluid which is actually discharged fromthe cylinder 1 or 20 flows into the fluid supply and discharge tank 18to mingle with a comparatively cool brake fluid therein. When the brakesare applied next, a part of the brake fluid which has been mixed in thefluid supply and discharge tank 18 to be comparatively cool actuallyflows into the cylinder 1 or 20 so as to be mixed with the brake fluidremaining therein, so that the brake fluid in the cylinder 1 or 20 isreduced in temperature. In this way, every time the brakes are appliedand released, a part of the brake fluid in the cylinder 1 or 20 isreplaced with the comparatively cool brake fluid in the fluid supply anddischarge tank 18 so that the temperature rise of the brake fluid in thecylinder 1 or 20 is restrained. Moreover, accompanying the release ofthe brakes, a part of the brake fluid in the fluid supply and dischargetank 18, i.e., a brake fluid as much as that actually discharged fromthe cylinder 1 or 20 at the time of releasing the brakes flows into thesecond main fluid channel 6b, and flows into the fluid supply anddischarge tank 18 at the time of applying the brakes.

Therefore, the volume of the brake fluid capable of taking part in thecylinder 1 or 20 for operating the brakes is limited to the capacity ofthe cylinder in the conventional brake operating unit, while it becomesthe capacity of the cylinder 1 or 20+the capacity D of the first mainfluid channel 6a+the capacity C of the fluid supply and discharge tank18 according to the present invention, so that it is not only increasedby the capacity D of the first main fluid channel 6a+the capacity C ofthe fluid supply and discharge tank 18, but also the brake fluid iscooled by air also in the first main fluid channel 6a and the fluidsupply and discharge tank 18 so as to promote a temperature decrease ofthe brake fluid in the cylinder 1 or 20. As a result, the brake fluid inthe cylinder 1 or 20 is prevented from being overheated by heatgenerated accompanying the operation of the brakes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a first embodiment of theinvention;

FIG. 2 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a second embodiment of theinvention;

FIG. 3 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a third embodiment of theinvention;

FIG. 4 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a fourth embodiment of theinvention;

FIG. 5 is a cross-sectional view showing a structure of a check valve;

FIG. 6 is a cross-sectional view showing the other structure of thecheck valve;

FIG. 7 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a fifth embodiment of theinvention;

FIG. 8 is a view showing a brake operating unit equipped with a devicefor cooling a brake fluid according to a sixth embodiment of theinvention;

FIG. 9 is a view for explaining the application of the device forcooling a brake fluid in FIG. 8;

FIG. 10 is a view for explaining a structure of a fluid supply anddischarge tank in FIG. 8;

FIG. 11 is a view for explaining the other structure of the fluid supplyand discharge tank in FIG. 8;

FIG. 12 is a cross-sectional view of a tank shown in FIGS. 1, 2, 3, 4and 7;

FIG. 13 is a cross-sectional view of a first and a second flow channelsshown in FIGS. 1, 2, 3, 4 and 7;

FIG. 14 is a view showing a first and a second flow channels equippedwith a connecting member;

FIG. 15 is a view showing the first and second flow channels equippedwith a connecting member having another structure; and

FIG. 16 is a cross-sectional view of the first and second flow channelsequipped with a connecting member having still another structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the invention will be described hereinafterwith reference to drawings.

FIG. 1 shows a device for cooling a brake fluid according to a firstembodiment of the invention applied to a drum brake unit. In the figure,denoted at 1 is a cylinder of a brake element (a drum brake), i.e., awheel cylinder of a drum brake for a vehicle. A pair of pistons 16 and17 are slidably fitted into the cylinder 1 for expanding a distancebetween a pair of brake shoes, not shown. First and second flow channels2 and 3, at respective one ends thereof, are connected to the pressurechamber of the cylinder 1 of the brake element and are merged into oneend of a main fluid channel 6 at the other ends thereof and are furtherconnected to the pressure chamber of a fluid (liquid) pressuregenerating unit 5 composed of, e.g., a master cylinder by way of themain fluid (liquid) channel 6. The first and second flow channels 2 and3 and the merging portion of the main fluid channel 6 at one end portionthereof are flexible to permit the relative vertical movement betweenthe chassis (body) of the vehicle and the non-suspended portion thereof.Denoted at 15 is a brake pedal.

The fluid pressure generating unit 5 comprises a booster of a servobrake and a brake valve for a full-power brake other than the mastercylinder. The servo brake makes use of fluid pressure generated byvacuum, compressed air or a hydraulic pump. As boosters for the servobrake there are a hydraulic vacuum servo and a hydraulic air servosystems disposed between the master cylinder and the cylinder 1, an airover hydraulic booster disposed between an air brake valve and thecylinder 1 and the like. The full power brake supplies a pressurizedfluid (liquid) generated by a pump to the cylinder 1 under control of abrake valve interlocked with the depressed amount of the brake pedal 15so as to generate a braking force.

The first flow channel 2 is provided with a check valve 7 interposedtherein as a means for generating a difference between the amount ofbrake fluid supplied to the cylinder 1 accompanying the application ofthe brakes and the amount of brake fluid discharged from the cylinder 1accompanying the release of the brakes. The check valve 7 provided inthe first flow channel 2 permits the flowing amount a₂ of brake fluidinto the cylinder 1 from the fluid pressure generating unit 5 andrestrains the flowing amount of brake fluid from the cylinder 1 towardthe fluid pressure generating unit 5 (a flow in a direction reverse tothat of the flowing amount a₂). A normal check valve can be used as thecheck valve 7, and in addition to this, since it is desirable to permitthe flowing amount a₂ with resistance as little as possible, forexample, a device that is similar in structure to the primary cup of themaster cylinder can be fixed in the first flow channel 2 for thispurpose. The check valve 7 need not entirely shut off the flow in thereverse direction to that of the flowing amount a₂ but may be alsodesigned to restrain the flow partially.

A tank 8 for storing the brake fluid therein is provided in the firstflow channel 2 in series with the check valve 7. The tank 8 is providedfor increasing the amount of the circulating brake fluid by keeping backthe same, the tank 8 forming a part of the flow channel with an inletport 8a and an outlet port 8b which are disposed apart from each otherand at which the tank 8 is connected to the first flow channel 2. It isa matter of course that the tank 8 is larger in cross section than thefirst flow channel 2. It is also possible to integrally form the firstflow channel 2, the second flow channel 3 and the check valve 7 (as wellas the tank 8) into a single housing and fix the housing to anon-rotating portion of a vehicle such as the external surface of thecylinder 1, the back plate of a drum brake etc.

FIG. 5 shows a structure of a check valve 7. The check valve 7 composedof a plate-shaped valve body 7a made of rubber or elastomer which isbonded to the inner wall of the cylinder 1 at one end portion (left endportion in the figure) thereof is normally restored to the originalstate as indicated by a solid line in FIG. 5 by elasticity and gravityto close the first flow channel 2 while getting out of the strokes ofthe pistons 16 and 17. Whereas the valve body 7a is elastically deformedas indicated by a broken line in FIG. 5 to open the first flow channel 2so as to allow the brake fluid to flow into the cylinder 1 from thefluid pressure generating unit 5 as much as the flowing amount a₂ and isseated on the inner wall of the cylinder 1 to restrain the flow of thebrake fluid from the cylinder 1 toward the fluid pressure generatingunit 5 (a flow in a direction reverse to that of the flowing amount a₂).

FIG. 6 shows the other structure of the check valve 7. The check valve 7is composed of a valve seat 7b , which has a shape of a cone graduallyupwardly increasing in diameter and is provided at a middle portion ofan inclined first flow channel 2, and a valve body 7c which has a shapeof a ball and is disposed in the first flow channel 2 without beingurged by a spring so that it can be seated in the valve seat 7b. Thebrake fluid is allowed to flow into the cylinder 1 from the fluidpressure generating unit 5 as much as the flowing amount a₂ when thevalve body 7c is pushed up as illustrated by the broken line in FIG. 6to open the first flow channel 2, and is restrained from flowing fromthe cylinder 1 toward the fluid pressure generating unit 5 when thevalve body 7c is seated in the valve seat 7b by gravity to close thefirst flow channel 2.

When the brake pedal 15 is depressed in a brake operating unit equippedwith the device for cooling a brake fluid, the brake fluid pushed outinto the main fluid channel 6 from the fluid pressure generating unit 5and the brake fluid in the main fluid channel 6 is branched into thefirst and second flow channels 2 and 3, i. e., a part of the brake fluidflows into the cylinder 1 as much as the flowing amount a₂ through thefirst flow channel 2 by way of the tank 8 and the check valve 7, whilethe other part flows directly into the cylinder 1 as much as a flowingamount a₁ through the second flow channel 3. As a result, the pistons 16and 17 which are slidably fitted in the cylinder 1 are respectivelypushed out therefrom to expand a distance between a pair of brake shoes,not shown, to obtain a braking force.

Successively, when the brake is released, the brake fluid in thecylinder 1 flows back toward the fluid pressure generating unit 5. Atthat time, since the flow from the cylinder 1 toward the fluid pressuregenerating unit 5 is restrained by the check valve 7 in the first flowchannel 2, the brake fluid does not flow substantially therein, so thatit flows through the second flow channel 3 as much as a flowing amount band consequently the brake fluid is discharged through the second flowchannel 3 in large quantity compared with that supplied therethrough.Since the amount of the brake fluid supplied to the cylinder 1 issubstantially equal to that discharged therefrom in a cycle of applyingand releasing the brakes, the brake fluid in the cylinder 1 is replacedby the amount of b-a₁ in the cycle. A brake fluid is supplied to thecylinder 1 through the first flow channel 2 as much as the amount b-a₁of the brake fluid that flows out of the same. The brake fluid that hasflowed out of the cylinder 1 flows into the first flow channel 2 by wayof the second flow channel 3, pooled (stored) in the tank 8 and thenflows back to the cylinder 1 through the first flow channel 2 so as tocirculate for braking operation as the operation of the brakes isrepeated.

The brake fluid used in the cylinder 1 for operating the brakes isgradually cooled by air as it flows through the second flow channel 3,the tank 8 and the first flow channel 2 so as to be prevented from beingoverheated by heat generated accompanying the operation of the brakes.As a result, vapor-lock caused by the vaporization of the brake fluidcan be effectively prevented. Since the boiling point of the brake fluidwhen the same absorbs moisture (wet boiling point) is about 140° C., itis possible to prevent almost all the conventional vapor-lock by settingthe amount of the brake fluid in the second flow channel 3, the tank 8and the first flow channel 2 and the amount of replaced brake fluid sothat the brake fluid in the cylinder 1 is not overheated over 140° C.

The function of the device for cooling a brake fluid will be describedin detail hereinafter. The check valve 7 positively generates in thefirst flow channel 2 a difference between the amount of the brake fluidsupplied to the cylinder 1 accompanying the application of the brakesand that discharged from the cylinder 1 accompanying the release of thebrakes to increase the former. Due to the function of the check valve 7,the brake fluid is supplied to the cylinder 1 accompanying theapplication of the brake through both of the first and second flowchannels 2 and 3 while the brake fluid is discharged from the cylinder 1accompanying the release of the brakes through the second flow channel 3mainly so that in the second flow channel 3 the amount of the brakefluid discharged from the cylinder 1 becomes large in quantity comparedwith the amount of the brake fluid supplied to the cylinder 1. As aresult, a value of a difference between the amount of the brake fluidsupplied to the cylinder 1 accompanying the application of the brakesand the amount of the brake fluid discharged from the cylinder 1accompanying the release of the brakes in the first flow channel 2(which is equal to the amount of the brake fluid supplied to thecylinder 1 supposing that the back current of the check valve 7 is zero)is identical with the inversed value of a difference (a₁ -b) between theamount of the brake fluid supplied to the cylinder 1 accompanying theapplication of the brakes and the amount of the brake fluid dischargedfrom the cylinder 1 accompanying the release of the brakes through thesecond flow channel 3. That is, the absolute value of the differencebetween the amounts of supply and discharge in the first flow channel 2is equal to that in the second flow channel 3. Thus it is possible tocirculate the brake fluid in the cylinder 1 using both of the first andsecond flow channels 2 and 3.

As described above, the device for cooling a brake fluid of theinvention circulates the brake fluid in the cylinder 1 using the firstand second flow channels 2 and 3, so that nothing should intervene inone of the first and second flow channels 2 and 3 to impede thecirculation of the brake fluid other than the means for generating thedifference between the amount of the brake fluid supplied to thecylinder 1 accompanying the application of the brakes and the amount ofthe brake fluid discharged from the cylinder 1 accompanying the releaseof the brakes. Therefore, in case a safety cylinder which impedes thecirculation of the brake fluid is provided, the first and second flowchannels 2 and 3 are disposed at the side of the cylinder 1 relative tothe safety cylinder. The safety cylinder shuts off a fluid channel(brake line) at the side where the brake fluid is leaking to secure thefunction of other portions in the system in case the brake fluid leaks.

Incidentally, providing a cooling fin 23 on at least a part of the firstand second flow channels 2 and 3 further increases the effect of coolingthe brake fluid by air. It is possible to omit the tank 8 if the brakefluid is cooled sufficiently by the fin 23 while it flows in the firstand second flow channels 2 and 3. In case of providing the tank 8, itmay be provided where the brake fluid circulates, so that it can beprovided on the second flow channel 3 too. It is a matter of course thatthe cooling fin 23 can be provided on the tank 8, too. Moreover, theconnecting portions for connecting the one ends of the first and secondflow channels 2 and 3 to the cylinder 1 had better be apart from eachother as far as possible so that the brake fluid may flow into thecylinder 1 from the first flow channel 2 and flow out therefrom into thesecond flow channel 3 relatively smoothly for replacement withoutinterfering each other. However, it is also possible to form one endportions of the first and second flow channels 2 and 3 as one body whichis cylindrical in external shape and screw the united end portionsthereof into a portion of the cylinder 1. In this case, it is advisableto connect flexible pipes to at least one of the first and second flowchannels 2 and/or 3 for extending the same into the cylinder 1 so as toplace the inlet and the outlet apart from each other therein. It is amatter of course that the one ends of the first and second flow channels2 and 3 are connected to an or plural openings of the cylinder 1 whichis not closed by the pistons 16 and 17.

Although the check valve 7 is provided in the first flow channel 2 toallow the brake fluid to flow into the cylinder 1 from the fluidpressure generating unit 5 as much as the flowing amount a₂ and restrainthe flow of the brake fluid from the cylinder 1 toward the fluidpressure generating unit 5 (in a direction reverse to that of theflowing amount a₂) in the first flow channel 2 in the above embodiment,similar effect can be obtained also by omitting the check valve 7 andproviding the other check valve in the second flow channel 3 to therebyallow the brake fluid to flow into the cylinder 1 from the fluidpressure generating unit 5 as much as the flowing amount a₁ and restrainthe flow of the brake fluid from the cylinder 1 toward the fluidpressure generating unit 5 (in a direction reverse to that of theflowing amount a₁) in the second flow channel 3.

FIG. 2 shows a device for cooling a brake fluid according to a secondembodiment of the invention, wherein components substantially having thesame function as those of the first embodiment are denoted at the samenumerals and the explanations thereof are omitted. According to thesecond embodiment, a narrow portion 10 (contraction of area) is providedin the second flow channel 3 as a means for generating a differencebetween the amount of the brake fluid supplied to the cylinder 1accompanying the application of the brakes and the amount of the brakefluid discharged from the cylinder 1 accompanying the release of thebrakes. The narrow portion 10 restrains the fast flowing amount a₁ ofthe brake fluid into the cylinder 1 from the fluid pressure generatingunit 5 accompanying a normal application of the brakes and effectivelyallows a slow flowing amount b₁ of the brake fluid toward the fluidpressure generating unit 5 from the cylinder 1 accompanying the releaseof the brakes.

When the brake pedal 15 is depressed in the brake operating unitequipped with the device for cooling a brake fluid, the brake fluidstrongly pushed out into the main fluid channel 6 from the fluidpressure generating unit 5 mainly passes through the first flow channel2 to flow into the cylinder 1. That is, from the first flow channel 2the brake fluid freely flows into the cylinder 1 through the tank 8while from the second flow channel 3 the brake fluid is restrained fromflowing into the cylinder 1 by the narrow portion 10. In this way,mainly the brake fluid which flows into the cylinder 1 from the firstflow channel 2 pushes out the pistons 16 and 17 slidably fitted in thecylinder 1 to expand a distance between a pair of brake shoes, notshown, to obtain a braking force.

Successively, when the brakes are released, the brake fluid flows backtoward the fluid pressure generating unit 5 from the cylinder 1. At thattime, the brake fluid flows back through the first and second flowchannels 2 and 3 almost similarly. Since the narrow portion 10 in thesecond flow channel 3 provides a large resistance to a fast flow of thebrake fluid accompanying the normal depression of a brake pedal 15, butdoes not to the slow flow of the brake fluid accompanying the return ofthe pistons 16 and 17 by the resilience of a return spring, not shown,there positively occurs a difference between the amount of the brakefluid supplied to the cylinder 1 accompanying the application of thebrakes and the amount of the brake fluid discharged from the cylinder 1accompanying the release of the brakes in the second flow channel 3.

Accordingly, the brake fluid is supplied to the cylinder 1 accompanyingthe application of the brakes mainly through the first flow channel 2and is discharged from the cylinder 1 accompanying the release of thebrakes through both of the first and second flow channels 2 and 3, sothat the amount of the brake fluid discharged through the second flowchannel 3 becomes large in quantity compared with that suppliedtherethrough. As a result, the absolute value of a difference in thefirst flow channel 2 between the flowing amount a₂ of the brake fluidsupplied to the cylinder 1 accompanying the application of the brakesand the flowing amount b₂ of the brake fluid discharged from thecylinder 1 accompanying the release of the brakes becomes equal to theabsolute value of a difference in the second flow channel 3 between theflowing amount a₁ of the brake fluid supplied to the cylinder 1accompanying the application of the brakes and the flowing amount b₁ ofthe brake fluid discharged from the cylinder 1 accompanying the releaseof the brakes.

The brake fluid that has flowed into the cylinder 1 through the firstflow channel 2 gradually flows out through the second flow channel 3 bythe repetition of applying and releasing the brakes. The brake fluidthat has flowed out of the second flow channel 3 flows into the tank 8through the first flow channel 2 to be temporarily stored therein, thenflows into the cylinder 1 through the first flow channel 2 forcirculation. Thus the brake fluid that has been used in the cylinder 1for the application of the brakes is cooled by air while it flowsthrough the second flow channel 3, the tank 8 and the first flow channel2 so as to be prevented from being overheated by heat generatedaccompanying the operation of the brakes and obtain a similar effect tothe first embodiment.

FIG. 3 shows a device for cooling a brake fluid according to a thirdembodiment of the invention applied to a disc brake, and componentssubstantially having the same functions as those of the first embodimentare denoted at the same numerals and the explanations thereof areomitted. According to the third embodiment, one ends of the first andsecond flow channels 2 and 3 are connected to the pressurized chamber ofa cylinder 20 of a caliper in a disc brake unit. A piston 21 slidablyengages the cylinder 20. The cylinder 20 may be also of plural-pot typesuch as a two-pot type having a pair of pistons 21, further a three-pottype and the like. In case of the plural-pot type, the first and secondflow channels 2 and 3 are divided into the number of the plural pots atone ends thereof to be connected to the pots of the cylinder 20respectively. A check valve 11 is provided in the first flow channel 2for restraining the brake fluid from flowing into the cylinder 20 fromthe fluid pressure generating unit 5 and allowing the brake fluid toflow toward the fluid pressure generating unit 5 from the cylinder 20 asa means for generating a difference between the amount of the brakefluid supplied to the cylinder 20 accompanying the application of thebrakes and that discharged from the cylinder 20 accompanying the releaseof the brakes.

When a brake pedal 15 is depressed in the brake operating unit equippedwith the device for cooling a brake fluid, the brake fluid that has beenpushed out into the main fluid channel 6 from the fluid pressuregenerating unit 5 flows into the cylinder 20 through the second flowchannel 3 in large quantity. That is, the brake fluid freely flows intothe cylinder 20 through the second flow channel 3, but it is restrainedby the check valve 11 from flowing into the cylinder 20 through thefirst flow channel 2. Thus the large quantity of the brake fluid flowinginto the cylinder 20 through the second flow channel 3 pushes out thepiston 21 slidably engaging the cylinder 20 to obtain a braking force byway of a pair of pads of a disc brake, not shown.

Successively, when the brakes are released, the brake fluid flows backtoward the fluid pressure generating unit 5 from the cylinder 20. Atthat time, the brake fluid flows back almost similarly through both ofthe first and second flow channels 2 and 3. In this way, the amount ofthe brake fluid supplied to the cylinder 20 accompanying the applicationof the brakes is little in the first flow channel 2 due to the functionof the check valve 11, so that the amount of the brake fluid dischargedfrom the cylinder 20 accompanying the release of the brakes becomeslarger than that supplied to the cylinder 20 to positively generate adifference therebetween. As a result, the absolute value of a differencein the first flow channel 2 between the amount of the brake fluidsupplied to the cylinder 20 accompanying the application of the brakesand that discharged from the cylinder 20 accompanying the release of thebrakes becomes equal to the absolute value of a difference in the secondflow channel 3 between the amount of the brake fluid supplied to thecylinder 20 accompanying the application of the brakes and thatdischarged from the cylinder 20 accompanying the release of the brakes.

Accordingly, by the repetition of applying and releasing the brakes, thebrake fluid that has flowed into the cylinder 20 through the second flowchannel 3 gradually flows out from the first flow channel 2 to be storedin the tank 8, and thereafter flows back to the cylinder 20 through thesecond flow channel 3 for circulation. As a result, the brake fluid thathas been used in the cylinder 20 for applying the brakes is cooled byair while it flows through the first flow channel 2, the tank 8 and thesecond flow channel 3 so as to be prevented from being overheated andobtain a similar effect to that of the first embodiment.

Although the check valve 11 is provided in the first flow channel 2 forrestraining the brake fluid from flowing into the cylinder 20 from thefluid pressure generating unit 5 while allowing the brake fluid to flowtoward the fluid pressure generating unit 5 from the cylinder 20 in thefirst flow channel 2, it is also possible to obtain a similar effectalso by omitting the check valve 11 and providing the other check valein the second flow channel 3 for restraining the brake fluid fromflowing into the cylinder 20 from the fluid pressure generating unit 5while allowing the brake fluid to flow toward the fluid pressuregenerating unit 5 from the cylinder 20 in the second flow channel 3.

FIG. 4 shows a device for cooling a brake fluid according to a fourthembodiment of the invention and components substantially having the samefunctions as those of the first embodiment are denoted at the samenumerals and the explanations thereof are omitted. According to thefourth embodiment, a check valve 12 is provided in the first flowchannel 2 for allowing the brake fluid to flow from the fluid pressuregenerating unit 5 toward the cylinder 1 and restraining the brake fluidfrom flowing from the cylinder 1 toward the fluid pressure generatingunit 5 as a means for generating a difference between the amount of thebrake fluid supplied to the cylinder 1 accompanying the application ofthe brakes and that discharged from the cylinder 1 accompanying therelease of the brakes. Also a check valve 13 is provided in the secondflow channel 3 for restraining the brake fluid from flowing toward thecylinder 1 from the fluid pressure generating unit 5 and allowing thebrake fluid to flow toward the fluid pressure generating unit 5 from thecylinder 1 as a similar means. Moreover, the tank 8 for storing thebrake fluid therein is disposed at the other end portions of the firstand second flow channels 2 and 3, i.e., where they are connected to themain fluid channel 6.

When the brake pedal 15 is depressed in the brake operating unitequipped with the device for cooling a brake fluid, the brake fluidpushed out into the main fluid channel 6 from the fluid pressuregenerating unit 5 flows into the cylinder 1 in large quantity throughthe first flow channel 2. That is, from the first flow channel 2 thebrake fluid flows into the cylinder 1 through the check valve 12 whilefrom the second flow channel 3 the brake fluid is restrained fromflowing into the cylinder 1 by the check valve 13 . Thus the pistons 16and 17 slidably fitted in the cylinder 1 are pushed out to obtain abraking force by way of a pair of brake shoes of a drum brake, notshown.

Successively, when the brakes are released, the brake fluid flows backtoward the fluid pressure generating unit 5 from the cylinder 1. At thattime, the brake fluid in the cylinder 1 is restrained from flowing outtherefrom through the first flow channel 2 by the check valve 12 whilethe brake fluid in the cylinder 1 is allowed to flow out therefromthrough the second flow channel 3 in large quantity by the check valve13. In this way, the absolute value of a difference in the first flowchannel 2 between the amount of the brake fluid supplied to the cylinder1 accompanying the application of the brakes and that discharged fromthe cylinder 1 accompanying the releasing of the brakes becomes equal tothe absolute value of a difference in the second flow channel 3 betweenthe amount of the brake fluid supplied to the cylinder 1 accompanyingthe application of the brakes and that discharged from the cylinder 1accompanying the releasing of the brakes.

By the repetition of applying and releasing the brakes, the brake fluidthat has flowed into the cylinder 1 through the first flow channel 2gradually flows out from the second flow channel 3 to be pooled in thetank 8, and thereafter flows back to the cylinder 1 through the firstflow channel 2 for circulation. Accordingly, the brake fluid that hasbeen used in the cylinder 1 for the application of the brakes is cooledby air while it flows through the second flow channel 3, the tank 8 andthe first flow channel 2 so as to be prevented from being overheated andobtain a similar effect to that of the first embodiment. According tothe fourth embodiment, however, the brake fluid is supplied to thecylinder 1 through the first flow channel 2 in large quantity and isdischarged therefrom through the second flow channel 3 in largequantity, so that the brake fluid in the cylinder 1 is replaced rapidly.As a result, the brake fluid in the cylinder 1 is effectively preventedfrom being overheated. Incidentally, it is not always necessary for thecheck valves 12 and 13 to completely shut off the backward flows so longas the brake fluid flows through the first flow channel 2 into thecylinder 1 in large quantity compared with the amount of discharge andis discharged through the second flow channel 3 from the cylinder 1 inlarge quantity compared with the amount of supply.

Although the first and second flow channels 2 and 3 are connected to thefluid pressure generating unit 5 by way of the main fluid channel 6according to the first to fourth embodiments set forth above, it is alsopossible to obtain a similar effect with respect to the circulation ofthe brake fluid by omitting the main fluid channel 6 and directlyconnecting the first and second flow channels 2 and 3 to the fluidpressure generating unit 5. Moreover, the present invention is alsoapplicable to a brake operating unit equipped with an anti-skid brakingsystem. In this case, the first and second flow channels 2 and 3 aredisposed at the side of the cylinder 1 or 20 relative to a pressureadjusting unit 18 equipped with a pump, an electromagnetic valve, etc.for making the brake fluid circulate in case the brake fluid isdischarged toward the pressure adjusting unit and also it is supplied tothe cylinder 1 or 20 from the pressure adjusting unit. Furthermore, itis also possible to obtain a function substantially similar to those ofthe first to fourth embodiments set forth above by providing theplurality of check valves 7, 11 or 12 in the first flow channel 2,and/or providing the plurality of narrow portions 10 or check valves 13in the second flow channel 3.

According to the first to fourth embodiments, similarly to the fifthembodiment described later, the tank 8 has a structure as illustrated inFIG. 12. That is, the tank body 80 of the tank 8 is divided inside intoa plurality of liquid chambers 80a(, 80b) and 80c by at least (two inthis embodiment) a partition 81 (and 82), neighboring liquid chambers80a(, 80b) and 80c communicating with each other by way of at least a(or plural) opening portion(s) 81a(and 82a respectively). The liquidchamber 80a located at one end of the tank body 80 is connected to oneof the first and second flow channels 2 and 3 at the hot side while theliquid chamber 80c located at the other end of the tank body 80 isconnected to one of the first and second flow channels 2 and 3 at thecool side. That is, in case of the tank 8 illustrated in FIGS. 1 to 3respectively showing the first to third embodiments, the liquid chambers80a and 80c located at both ends of the tank body 80 are connected tothe first flow channel 2 as illustrated in FIG. 12. In case of the tank8 according to the fourth embodiment as illustrated in FIG. 4, theliquid chamber 80a located at one end of the tank body 80 is connectedto the second flow channel 3 at the hot side, while the liquid chamber80c located at the other end of the tank body 80 is connected to thefirst flow channel 2 at the cool side. The tank body 80 of the tank 8 isfixed to a body 83 of the vehicle having a comparatively low temperatureof a vehicle in a state wherein the former contacts with the latter overan area as large as possible.

In case one end of the main fluid channel 6 is connected to the tank 8like the fourth embodiment as illustrated in FIG. 4, one of the liquidchambers 80a, 80b and 80c may be connected to the main fluid channel 6.As a result, a part of the brake fluid in one of the liquid chambers80a, 80b and 80c that flows into the main fluid channel 6 when thebrakes are released is effectively cooled by air in the main fluidchannel 6. Moreover, if the second flow channel 3 at hot side instead ofthe first flow channel 2 as well as the main fluid channel 6 indicatedby a chain line in FIG. 12 are connected to the liquid chamber 80alocated at one end of the tank body 80, a part of the brake fluid in theliquid chamber 80a into which a hot brake fluid flows from the cylinder1 and which is in a state of high temperature flows into the main fluidchannel 6 to be effectively cooled by air therein when the brakes arereleased.

As for the tank 8 described above, the hot brake fluid flowing out fromthe cylinder 1 or 20 enters the liquid chamber 80a located at one end ofthe tank body 80 by way of the first flow channel 2 or the second flowchannel 3 at hot side, gradually flows into the central liquid chamber80b through the opening portion 81a accompanying the repetition ofapplying and releasing the brakes, further flows into the liquid chamber80c located at the other end of the tank body 80 gradually through theopening portion 82a and flows out through the first flow channel 2 (orthe second flow channel 3) at the cool side. Hereby, the brake fluidthat is cooled by air in the tank 8 is gradually reduced in temperatureas it flows through the liquid chambers 80a, 80b and 80c and the cooledbrake fluid flows out through the first flow channel 2 (or the secondflow channel 3) at the cool side for circulation. As a result, the coolbrake fluid flows into the cylinder 1 or 20 so as to effectively preventthe brake fluid in the cylinder 1 or 20 that is a brake element frombeing overheated by heat accompanying the operation of the brakes.Moreover, since the tank body 80 of the tank 8 is fixed to the body 83,the body 83 serves as a radiating fin to effectively cool the brakefluid in the tank 8. Contact between the tank 8 and the body 83 over anarea as large as possible effects good conduction of heat.

Furthermore, if the first flow channel 2 or the second flow channel 3 atthe hot side is connected to the upper end portion of the liquid chamber80a located at one end of the tank body 80, the first flow channel 2 (orthe second flow channel 3) at the cool side is connected to the lowerend portion of the liquid chamber 80c located at the other end of thetank body 80 and the opening portions 81a and 82a is formed in the lowerend portions of the liquid chambers 80a, 80b and 80c which is low intemperature so as to be apart from the portions of the tank body 80 towhich the first flow channel 2 or the second flow channel 3 isconnected, the hot brake fluid flowing into the upper end portion of theliquid chamber 80a located at one end of the tank body 80 from the firstflow channel 2 or the second flow channel 3 at the hot side is preventedfrom keeping the high temperature when it flows into the central liquidchamber 80b, and still furthermore, the brake fluid of low temperaturein the lower end portion of the liquid chamber 80c located at the otherend of the tank body 80 flows out through the first flow channel 2 atthe cool side, so that the brake fluid can be effectively reduced intemperature in the tank 8. It is a matter of course that the openingportions 81a and 82a had better be formed apart from each other. It isalso possible to arrange the first flow channel 2 or the second flowchannel 3 at the hot side and the second flow channel 3 at the cool sidedepending on the arrangement of the means 7, 10, 11, or 12 and 13 or thenarrow portion 10.

If the tank body 80 is made of metal and the partitions 81 and 82 aremade of a material having small heat conductivity other than metals,e.g., synthetic resin, radiation of heat from the tank body 80 ispromoted and conduction of heat between neighboring liquid chambers 80a,80b and 80c defined by the partitions 81 and 82 is restrained to keepthe differences of temperature between the brake fluids in adjacentliquid chambers 80a(, 80b) and 80c. As a result, the brake fluid flowingout from the first flow channel 2 (or the second flow channel 3) at thecool side can be effectively reduced in temperature. It is also possibleto provide the means 7, 10, 11, or 12 and 13 or the narrow portion 10attached to the tank 8 so as to make the brake operating unit compact.

Still furthermore, it is also possible to provide a or a plurality oftanks 8 in which at least a tank 8 may have a tank body 80 dividedinside into a plurality of liquid chambers 80a, 80b and 80c and othertanks 8 may have a single liquid chamber, or one or all tanks 8 may becomposed of oil coolers having the well-known structure for cooling thebrake fluid.

In case the first flow channel 2 and the second flow channel 3 are madeof flexible brake (rubber) hoses at least at one end portions thereof,i.e., at the side of the cylinder 1 or 20 to permit a relative verticalmovement between the chassis of a vehicle and the non-suspended portionthereof, the adjacent facing flexible portions of the first and secondflow channels 2 and 3 are connected to each other by way of a flexibleconnecting member 84 as illustrated in FIGS. 13 and 14. In concrete, theouter rubber covers of the first and second flow channels 2 and 3 eachmade of a brake hose are connected to each other by way of theconnecting member 84 mainly made of rubber or elastomer. Hereby thefirst and second flow channels 2 and 3 are kept apart from each other ata given interval by the connecting member 84, so that the first andsecond flow channels 2 and 3 can be prevented from mutual friction andabrasion while being flexible. As illustrated in FIG. 14, the connectingmember 84 having a plurality of opening portions 85 therein formedbetween the first and second flow channels 2 and 3 over the whole lengththereof in the axial direction can have a cooling function by way of theopening portions 85 while effectively securing the connecting functionbetween the first and second flow channels 2 and 3.

As illustrated in FIG. 15, a plurality of connecting members 84₁, 84₂ ,84₃, 84₄, 84₅ and 84₆ arranged between the first and second flowchannels 2 and 3 at given intervals in the axial direction thereof canreduce in mass and weight the connecting member 84 by the omittedportions and can restrain the temperature rise of the first and secondflow channels 2 and 3 at the cool side due to the reduction of heatconduction by way of the connecting members 84₁, 84₂, 84₃, 84₄, 84₅ and84₆ between the first and second flow channels 2 and 3 having atemperature difference. In order to reconcile reducing heat conductionthrough the connecting members 84₁, 84₂, 84₃, 84₄, 84₅ and 84₆ andsecuring the connecting performance and promote the reduction intemperature of the brake fluid flowing into the cylinder 1 or 20 fromthe first flow channel 2 or the second flow channel 3 at the cool side,it is desirable to set the intervals among the adjacent connectingmembers 84₁, 84₂, 84₃, 84₄, 84₅ and 84₆ in such a way that the intervalsfar from the cylinder 1 or 20 is smaller than those close thereto.

When the flexible first and second flow channels 2 and 3 are connectedto each other by way of connecting members 84a and 84b disposed apartfrom each other in the radial direction of cross sections of the firstand second flow channels 2 and 3 as illustrated in FIG. 16, theconnecting members 84a and 84b each having a small cross section effectgood connecting performance and further reduce heat conduction. The pairof connecting members 84a and 84b disposed in the radial direction ofcross sections of the first and second flow channels 2 and 3 can be alsoarranged to be shifted relative to each other in the axial direction ofthe first and second flow channels 2 and 3. As described above, it isalso possible to connect the first and second flow channels 2 and 3together by a connecting member made of an inflexible material whilesecuring the flexibility of the first and second flow channels 2 and 3if the connecting member is divided into a plurality of connectingmembers 84₁, 84₂, 84₃, 84₄ 84₅ and 84₆, or 84a and 84b in this way.

FIG. 7 shows a device for cooling a brake fluid according to a fifthembodiment of the invention and components substantially having the samefunctions as those of the first embodiment are denoted at the samenumerals and the explanations thereof are omitted. According to thefifth embodiment, the first flow channels 2 and 2' and the second flowchannels 3 and 3' are respectively connected at respective one endsthereof to the cylinders 1 and 1' of drum brakes, which are eachprovided at either the pair of front wheels or the pair of rear wheels,while the other ends of the first flow channels 2 and 2' mergingtogether and the other ends of the second flow channels 3 and 3' mergingtogether are connected to each other by way of a first connecting flowchannel 31 and a second connecting flow channel 32 connected to eachother in series. The first and second connecting flow channels 31 and 32form a part of the second flow channels 3 and 3'.

A closing valve unit 34 is interposed between the other ends of thesecond flow channels 3 and 3' merging together and one end of the firstconnecting flow channel 31 and between the other end of the firstconnecting flow channel 31 and one end of the second connecting flowchannel 32 to open and close the former and the latter channelsconcurrently, and a pump 33 is interposed in the first connecting flowchannel 31 for pumping the brake fluid from the second flow channels 3and 3' toward the first flow channels 2 and 2'. The closing valve units34, which is an open-close changeover valve, more in concrete, a slidespool valve composed of two 2-port/2-position selectors, concurrentlyopen a channel between the second flow channels 3 and 3' and the firstconnecting flow channel 31 and that between the first connecting flowchannel 31 and the second connecting flow channel 32 at an openingposition a and concurrently closes the same at a closing position b.Accordingly, it means that the closing valves are provided at both ofthe inlet 33a side and the outlet 33b side of the pump 33. Accordingly,the two closing valves disposed at the inlet 33a side and the outlet 33bside of the pump 33 can also obtain a function similar to that of thesingle closing valve unit 34 set forth above. Moreover, the tank 8 forpooling the brake fluid therein is provided in the second connectingflow channel 32.

When the pump 33 is actuated with the closing valves 34 at the openingposition a, the brake fluid in the cylinders 1 and 1' pass through thesecond flow channels 3 and 3' respectively and through the first andsecond connecting flow channels 31 and 32 successively to be stored inthe tank 8, then flows into the first flow channels 2 and 2' from theother ends thereof to flow back to the cylinders 1 and 1'. Accordingly,it is possible to circulate the brake fluid in the cylinders 1 and 1'using both of the first flow channels 2 and 2' and the second flowchannels 3 and 3'(and 31 and 32). Since the amount of the brake fluidtaken into the inlet 33a of the ump 33 is equal to that discharged fromthe outlet 33b of the pump 33, the mount of the brake fluid is notfluctuated in the cylinders 1 and 1' and the fluid pressure generatingunit 5 by actuating the pump 33.

As described above, the brake fluid used in the cylinders 1 and 1' forthe operation of the brakes is cooled by air while it passes through thesecond flow channels 3 and 3', the first and second connecting flowchannels 31 and 32, the tank 8 and the first flow channels 2 and 2' soas to be prevented from being overheated by heat accompanying theoperation of the brakes, so that a similar effect to the firstembodiment can be obtained. According to the fifth embodiment, however,the replaced amount of the brake fluid in the cylinders 1 and 1' dependson the amount of the brake fluid which flows into the inlet 33a of thepump 33 and flows out from the outlet 33b thereof, i.e., the operatingtime of the pump 33, so that the brake fluid in the cylinders 1 and 1'is effectively prevented from being overheated by adjusting theoperating time of the pump 33. It is a matter of course that asufficient amount of the brake fluid is accommodated in the second flowchannels 3 and 3', the first and second connecting flow channels 31 and32, the tank 8 and the first flow channels 2 and 2'. The fifthembodiment is also applicable to a single cylinder 1. At that time theother cylinder 1' and the first flow channel 2' and second flow channel3' which are connected to the other cylinder 1' are omitted.

Such a device for cooling a brake fluid as described above is suitablefor a brake operating unit equipped with an anti-skid braking system. Inthis case, a pump in a pressure adjusting unit of the anti-skid brakingsystem can be used as the pump 33. As a matter of course, the brakefluid cooling unit is operated while preventing the flow of the brakefluid for the anti-skid braking system by a closing valve, not shown,when the anti-skid braking system s not operated. The operation of theanti-skid braking system is secured by setting the closing valve unit 34to the closing position b.

The device for cooling a brake fluid should be operated when the brakepedal 15 is released from being depressed and, e.g., (1) the brake fluidin the cylinders 1 and 1' is directly or indirectly detected to be abovea given temperature (e.g., 100° C.), (2) the frequency of depression ofthe brake pedal 15 per unit time exceeds a given frequency, (3) thenumber of depression of the brake pedal 15 exceeds a given numberirrespective of the length of time, (4) every given time while theengine is driven, and the like. Needless to say, it is possible toobtain a similar effect in case the brake fluid is pumped toward thesecond flow channels 3 and 3' from the first flow channels 2 and 2' bythe pump 33. It is also possible to obtain a similar effect by providingan individual pump 33 at each of the cylinders 1 and 1' and actuatingthe same. Moreover, it is also possible to obtain a similar effect withregard to the circulation of the brake fluid by omitting the main fluidchannel 6 to directly connect the first flow channel 2 and the secondconnecting flow channel 32 to the fluid pressure generating unit 5. Itis also possible to discharge the brake fluid in the cylinders 1 and 1'through the second flow channels 3 and 3' to introduce the same into aor plurality accumulators, not shown, and return the brake fluid in theaccumulator to the first flow channels 2 and 2' by actuating the pump 33in order to prevent the wheels from being locked in the anti-skidbraking system. Furthermore, in the first to fifth embodiments, at leastone of the first flow channels 2 and 2' and/or the second flow channels3 and 3' can also be composed of a plurality of lines to obtain asimilar effect with regard to the circulation of the brake fluid.

FIGS. 8 and 9 shows a device for cooling a brake fluid according to asixth embodiment of the invention and components substantially havingthe same functions as those of the first embodiment are denoted at thesame numerals and the explanations thereof are omitted. According to thesixth embodiment, the first and second flow channels 2 and 3 are omittedand the main fluid channel 6 composed of the first and second main fluidchannels 6a and 6b is connected to the cylinder 1 at one end thereof andinterposes the fluid supply and discharge tank 18 therein. That is, thefirst main fluid channel 6a is connected to the pressure chamber of thecylinder 1 at one end thereof and to the fluid supply and discharge tank18 at the other end thereof, and the second main fluid channel 6b isconnected to the fluid supply and discharge tank 18 at one end thereofand to the pressure chamber of the fluid pressure generating unit 5 atthe other end thereof. The fluid supply and discharge tank 18 isprovided for the purpose of mixing up therein the brake fluid to besupplied to the cylinder 1, wherein an entrance 18a that is a connectingportion to the first main fluid channel 6a at the side of the cylinder 1and an entrance 18b that is a connecting portion to the second mainfluid channel 6b at the side of the fluid pressure generating unit 5 areseparately provided apart from each other and the fluid supply anddischarge tank 18 constitutes a part of the main fluid channel 6. Thecross-sectional area of the fluid supply and discharge tank 18 is set tobe at least larger than (preferably more than twice as large as) that ofthe first main fluid channel 6a.

The capacity of the first main fluid channel 6a is set so that a part ofthe brake fluid actually discharged from the cylinder 1 when the brakesare released can flow into the fluid supply and discharge tank 18 andthe capacity of the fluid supply and discharge tank 18 is set so thatthe fluid supply and discharge tank .18 may not be filled with the brakefluid actually discharged from the cylinder 1 when the brakes arereleased. As a result, it does not occur that the brake fluid actuallydischarged from the cylinder 1 when the brakes are released fills thefluid supply and discharge tank 18 and thereafter flows out therefromthrough the second main fluid channel 6b. Accordingly, a part of thebrake fluid actually discharged from the cylinder 1 when the brakes arereleased flows into a part of the fluid supply and discharge tank 18 tobe mixed with brake fluid remaining therein, and when the brakes areapplied next, the mixed brake fluid in the fluid supply and dischargetank 18 flows back into the cylinder 1.

Hereupon, the following relations are given assuming that the capacityof the pressure chamber of the cylinder 1 is A when the brakes arereleased wherein a pair of pistons 16 and 17 are contracted into thecylinder 1 as illustrated in FIG. 8, the capacity of the pressurechamber of the cylinder 1 is B when the brakes are applied wherein apair of pistons 16 and 17 are protruded as illustrated in FIG. 9, thecapacity of the fluid supply and discharge tank 18 is C and the capacityof the first main fluid channel 6a is D. When the capacities A and B ofthe pressure chambers of the cylinder 1 fluctuates due to the abrasionof friction members of brake shoes, they are set to values with dueconsideration of the fluctuation.

That is, it is desirable that the capacity D of the first main fluidchannel 6a is as small as possible (the first main fluid channel 6a isas short as possible) for mixing the brake fluid (B-A) actuallydischarged from the cylinder 1 when the brakes are released with thebrake fluid in the fluid supply and discharge tank 18. Therefore, thecapacity D of the first main fluid channel 6a is set to 9/10 of (B-A) atmaximum, preferably less than 3/5 , more preferably less than 1/2thereof so that it is set that the brake fluid amounting to more than1/10 , or more than 2/5 or more than 1/2 of the amount (B-A) of thebrake fluid actually discharged from cylinder 1 when the brakes arereleased may actually flow into the fluid supply and discharge tank 18.In this way, a part (substantially more than 1/10˜1/2) of the brakefluid actually discharged from the cylinder 1 when the brakes arereleased flows into a part of the fluid supply and discharge tank 18 tobe mixed with brake fluid remaining therein, and when the brakes areapplied next, the mixed brake fluid in the fluid supply and dischargetank 18 flows back into the cylinder 1 as much.

The capacity C of the fluid supply and discharge tank 18 is desirable tobe as large as possible for restraining the temperature rise of thebrake fluid in the fluid supply and discharge tank 18, at least as largeas to satisfy C>(B-A), preferably more than 1.5 (B-A), more preferablymore than 2 (B-A) so as to increase the amount of the brake fluidcapable of participating in the application of the brakes in thecylinder 1 to (B+D+C). Incidentally, the amount of the brake fluidcapable of participating in the application of the brakes in thecylinder 1 in a conventional brake element is limited by the capacity Bof the pressure chamber of the cylinder so that it is impossible toincrease the amount of the brake fluid capable of participating in theapplication of the brakes in the cylinder 1 so long as the cylinder 1 isnot enlarged.

When the brake pedal 15 is depressed in a brake operating unit equippedwith the device for cooling a brake fluid, the brake fluid pushed outinto the main fluid channel 6 from the fluid pressure generating unit 5flows into the cylinder 1 through the second main fluid channel 6b, thefluid supply and discharge tank 18 and the first main fluid channel 6a.

As a result, the pistons 16 and 17 slidably engaging the cylinder 1 arepushed out to operate a pair of brake shoes, not shown, to obtain abraking force. At that time, a part of the brake fluid in the fluidsupply and discharge tank 18 actually flows into the cylinder 1.

Successively, when the brakes are released, the brake fluid flows backfrom the cylinder 1 toward the fluid pressure generating unit 5. At thattime, a part of the brake fluid actually discharged from the cylinder 1flows into the fluid supply and discharge tank 18 to be mixed with thebrake fluid having a comparatively low temperature therein so that itbecomes comparatively low in temperature. When the brakes are appliednext, a part of the brake fluid having a comparatively low temperaturein the fluid supply and discharge tank 18 actually flows into thecylinder 1 to be mixed with the brake fluid therein, so that the brakefluid in the cylinder 1 is reduced in temperature.

As described above, every time when the brakes are applied and released,a part of the brake fluid in the cylinder 1 is replaced with the brakefluid having a comparatively low temperature in the fluid supply anddischarge tank 18 so that the temperature of the brake fluid in thecylinder 1 is restrained from rising. Moreover, accompanying the releaseof the brakes, a part of the brake fluid in the fluid supply anddischarge tank 18, i.e., the brake fluid (B-A) as much as that actuallydischarged from the cylinder 1 when the brakes are released flows intothe second main fluid channel 6b and flows back into the fluid supplyand discharge tank 18 when the brakes are applied. The amount of thebrake fluid flowing into or out of the second main fluid channel 6b isequal to that flowing in a conventional brake hose (fluid channel). As aresult, not only the amount of the brake fluid capable of participatingin the application of the brakes in the cylinder 1 is increased, butalso is cooled by air in the first main fluid channel 6a and the fluidsupply and discharge tank 18 too, so as to promote a decrease intemperature of the brake fluid in the cylinder 1.

As described above, the brake fluid in the cylinder 1 is effectivelyprevented from being overheated by heat accompanying the operation ofthe brakes. As a result, it is possible to obtain almost similar effectto the first embodiment with respect to the decrease in temperature ofthe brake fluid in the cylinder 1. According to the sixth embodiment,however, being different from the first to fifth embodiments, the brakefluid does not circulate but directly flows into the cylinder 1 afterhaving been mixed in the fluid supply and discharge tank 18, so that alarge decrease in temperature of the brake fluid cannot be expected.Therefore, it is suitable for a vehicle which is comparatively light anddoes not require a large braking force, in concrete, an ordinarypassenger car.

FIG. 10 shows a structure of the fluid supply and discharge tank 18. anentrance 18a that is a connecting portion to the first main fluidchannel 6a at the side of the cylinder 1 and an entrance 18b that is aconnecting portion to the second main fluid channel 6b at the side ofthe fluid pressure generating unit 5 are provided in the fluid supplyand discharge tank 18 to diagonally confront each other therein. As aresult, the brake fluid flows into the fluid supply and discharge tank18 through the pair of entrances 18a and 18b to generate a whirlpooltherein so as to be mixed well. FIG. 11 shows the other structure of thefluid supply and discharge tank 18, wherein a plate-shaped flowrestricting member 19 is provided aslant between the pair of entrances18a and 18b. In the fluid supply and discharge tank 18 having thisstructure, the brake fluid flowing thereinto runs against the flowrestricting member 19 to be dispersed therein so that the comparativelyhot brake fluid flowing into the fluid supply and discharge tank 18through the entrance 18a at the cylinder 1 side is prevented fromdirectly flowing out through the same entrance 18a. It is also possibleto provide a plurality of flow restricting members 19 in the fluidsupply and discharge tank 18 for dispersing the brake fluid flowingthereinto.

It is also possible to integrally form the first main fluid channel 6aand the fluid supply and discharge tank 18 of a hard material, e.g.,metal and fix one end portion of the first main fluid channel 6a to theouter wall of the cylinder 1. At that time, if the fluid supply anddischarge tank 18 is disposed at a position higher than the cylinder 1,the comparatively hot brake fluid in the cylinder 1 flows into the fluidsupply and discharge tank 18 through the first main fluid channel 6a bynatural convection. It is also possible to form the first main fluidchannel 6a larger in diameter than the second main fluid channel 6b orin a tapered shape, i.e., gradually increased in diameter toward thefluid supply and discharge tank 18 to form a part of the fluid supplyand discharge tank 18 so as to set the capacity D of the first mainfluid channel 6a substantially to zero. Moreover, it is also possible topositively reduce the temperature of the brake fluid in the cylinder 1by transferring heat between the brake fluids in the cylinder 1 and thefluid supply and discharge tank 18 by way of a heat transferring devicesuch as a heat pipe etc. slidably inserted into the first main fluidchannel 6a leaving a gap therebetween. It is also a matter of coursethat the fluid supply and discharge tank 18 can be fixed to anonrotating portion of a vehicle such as a back plate of a drum brake (abaffleplate in case of a disc brake). In case of a floating-caliper-typedisc brake, however, since a caliper forming a cylinder movesaccompanying the operating of the brakes, the first main fluid channel6a should be made flexible when it is fixed to a nonrotating portion ofa vehicle such as a baffleplate etc. other than the caliper.

As described above, it is a matter of course that not only the sixthembodiment but the first, second, fourth and fifth embodiments are alsoapplicable to a disc brake. In case the brake element is a disc brake,the cylinder 1 is formed in a caliper as the cylinder 20. Moreover, thethird embodiment is also applicable to a drum brake. In case the brakeelement is the drum brake, the cylinder 20 is attached to the back plateas the cylinder 1.

As understood from the above description, the method of and device forcooling a brake fluid according to the invention can obtain thefollowing effects.

(1) Since the brake fluid capable of participating in the application ofthe brakes in the cylinder of a brake element, i.e., a drum brake or adisc brake can be increased and effectively cooled by air, it ispossible to effectively prevent the brake fluid in the cylinder frombeing overheated without enlarging the cylinder of a brake element. As aresult, almost all the conventional vapor-lock can be prevented withcertainty without largely changing a design such as enlarging a brakeelement to eliminate brake operation failure, so that the brake elementis improved in safety remarkably as well as in reliability by acomparatively simple structure.

(2) Since the cylinder itself is also prevented from being overheated bya decrease in temperature of the brake fluid in the cylinder of a brakeelement, a friction material forming brake shoes or pads is alsorestrained from rising in temperature. As a result, fade phenomenon thatthe coefficient of friction of a friction material is reducedaccompanying the temperature rise thereof is also reduced so that astable braking operation is obtained.

(3) Moreover, according to the sixth or fourteenth aspect of theinvention, improving the cooling performance of the tank to further thetemperature decrease of the brake fluid which flows out therefrom caneffectively obtain the above effects. Furthermore, according to theseventh or fifteenth aspect of the invention, since the flexible firstand second flow channels are prevented from abrasion, it is possible toimprove the first and second flow channels in durability as well as toprevent accident caused by the leak of the brake fluid therefrom.

What is claimed is:
 1. A device for cooling brake fluid in a cylinder ofa brake element, comprising first and second flow channels wherein firstends of said first flow channel and second flow channel are connected tothe cylinder of the brake element, and second ends of said first flowchannel and second flow channel are connected to a fluid pressuregenerating unit which generates fluid pressure in accordance with adepressed amount of a brake pedal and at least one of said first andsecond flow channels is at least provided with means for generating adifference between an amount of brake fluid supplied to and an amountdischarged from said cylinder to apply and release said brakesrespectively through said first and second flow channels, wherein anabsolute value of a difference between an amount of said brake fluidsupplied to and an amount discharged from said cylinder in said firstflow channel is made equal to an absolute value of a difference betweenan amount of said brake fluid supplied to and an amount discharged fromsaid cylinder in said second flow channel so as to circulate said brakefluid in said cylinder using both of said first and second flowchannels, and a pressure adjusting unit including a pump which is remotefrom the brake cylinder and disposed in one of said first and secondflow channels, said pump circulating said brake fluid through said firstand second flow channels and the cylinder during a braking operation soas to prevent overheating of said brake fluid.
 2. A device for cooling abrake fluid according to claim, wherein a connecting member connectssaid first and second flow channels adjacent said first ends.
 3. Thedevice according to claim 2, wherein the connecting member is flexibleand portions of said first and second flow channels adjacent said firstends are flexible so that vertical movement between a vehicle chassisand brake cylinder can occur.
 4. The device for cooling brake fluidaccording to claim 2, wherein the connecting member extends axiallyalong the first and second flow channels and has a plurality of openingstherein for assisting in a cooling function.
 5. The device for coolingbrake fluid according to claim 2, wherein said connecting memberincludes first and second members connecting said first and second flowchannels, said first and second members being spaced from each other ina radial direction relative to said first and second flow channels.
 6. Adevice for cooling a brake fluid according to claim 1, wherein a tank isinterposed in said first and second flow channels for storing said brakefluid which circulates in said first and second flow channels, said tankforming a part of said first and second channels.
 7. A device forcooling a brake fluid according to claim 6, wherein said tank comprisesa tank body which is divided inside into a plurality of liquid chambersby at least a partition having an opening portion, wherein adjacentliquid chambers communicate with one another by way of said openingportion, one of said liquid chambers located at one end of said tankbody is connected to a hot side of one of said first and second flowchannels while a liquid chamber located at the other end of said tankbody is connected to a cool side of one of said first and second flowchannels.
 8. A device for cooling a brake fluid according to claim 6,characterized in that said means is attached to said tank.
 9. The devicefor cooling brake fluid according to claim 1, wherein a plurality ofconnecting members connects said first and second flow channels adjacentrespective said first ends thereof.
 10. The device for cooling brakefluid according to claim 9, wherein a plurality of intervals betweensaid plurality of connecting members increase in length away from saidfirst ends of said first and second flow channels.
 11. A device forcooling a brake fluid according to claim 4, wherein a main fluid channelis connected to the second ends of both of said first and second flowchannels and extends to said fluid pressure generating unit.
 12. Adevice for cooling a brake fluid according to claim 1, wherein saidcylinder is a plural-pot type for a disc brake.
 13. An anti-skid brakingsystem including a device for cooling brake fluid, comprising:a brakepedal movably connected to a vehicle; a fluid pressure generation unitconnected to said brake pedal and generating a fluid pressure inresponse to said brake pedal being depressed; first and second brakefluid flow channels fluidly connected at first ends thereof to saidfluid pressure generation unit; a brake element fluidly connected tosecond ends of said first and second channels, said brake system havinga brake release state with said fluid pressure generation unit notpressurizing brake fluid and said brake element not causing a brakingaction and a brake state with said fluid pressure generation unitflowing pressurized fluid into said first and second channels therebyactivating said brake element to effect a braking action; a flowrestriction device in said first channel reducing the amount of brakefluid flowing from said brake element through said first channel andincreasing the amount of brake fluid flowing through said second channelduring transition from said brake state to said brake release state sothat the brake fluid circulates through said brake system; and apressurized fluid circulating device positioned in at least one of saidfirst and second channels and during said brake state circulating brakefluid through said brake element and said first and second channels soas to prevent overheating of said brake fluid in said brake element. 14.The brake system according to claim 13, wherein a connecting memberconnects said first and second flow channels adjacent said second ends.15. The brake system according to claim 14, wherein the connectingmember is flexible and portions of said first and second flow channelsadjacent said second ends are flexible so that vertical movement betweena vehicle chassis and brake cylinder can occur.
 16. The brake systemaccording to claim 14, wherein the connecting member extends axiallyalong the first and second flow channels and has a plurality of openingstherein for assisting in a cooling function.
 17. The brake systemaccording to claim 14, wherein said connecting member includes first andsecond members connecting said first and second flow channels, saidfirst and second members being spaced from each other in a radialdirection relative to said first and second flow channels.
 18. The brakesystem according to claim 13, wherein a tank is interposed in said firstand second flow channels for storing said brake fluid which circulatesin said first and second flow channels, said tank forming a part of saidfirst and second channels.
 19. The brake system according to claim 16,wherein said tank comprises a tank body which is divided inside into aplurality of liquid chambers by at least a partition having an openingportion, wherein adjacent liquid chambers communicate with one anotherby way of said opening portion, one of said liquid chambers located atone end of said tank body is connected to a hot fluid side of one ofsaid first and second flow channels while another of said liquidchambers located at the other end of said tank body is connected to acool fluid side of said one of said first and second flow channels. 20.The brake system according to claim 18, wherein said flow restrictiondevice is attached to said tank.
 21. The brake system according to claim13, wherein a plurality of connecting members connects said first andsecond flow channels adjacent respective said second ends thereof. 22.The brake system according to claim 21, wherein a plurality of intervalsbetween said plurality of connecting members increase in length awayfrom said second ends of said first and second flow channels.
 23. Thebrake system according to claim 13, wherein a main fluid channel isconnected to the first ends of both of said first and second flowchannels and extends to said fluid pressure generating unit.
 24. Thebrake system according to claim 13, wherein said cylinder is aplural-pot type for a disc brake.